More Gram-Negative Rods

Bacteria 8: More Gram-Negative Rods

GNR Objectives

  • Outline and organize the following Gram-negative rods by specific criteria:
      - Pseudomonas
      - Burkholderia
      - Stenotrophomonas
      - Legionella
      - Fusobacterium

  • Criteria for organization include:
      - Biochemical testing
      - Morphology
      - Natural environment
      - Antibiotic resistance
      - Associated diseases

GNR Vocabulary

  • Key terms related to Gram-negative rods:
      - Sepsis
      - Endotoxin
      - Opportunistic
      - Pseudomonas aeruginosa:
        - Oxidase: positive
        - Non-fermenter: Aerobic
        - Exotoxin A: inhibits protein synthesis similar to diphtheria toxin
        - Pathologies: nosocomial infections, disease in cystic fibrosis, hot tub folliculitis, urinary tract infections (UTIs), antibiotic resistance
        - Other terms: Capsule, slime layer, biofilm
      - Burkholderia:
        - Burkholderia pseudo-mallei: causes melioidosis
      - Stenotrophomonas maltophilia: associated with pneumonia; treated with trimethoprim-sulfamethoxazole
      - Legionella: habitats include aquatic environments, associated with Legionnaires' disease and Pontiac fever
      - Buffered charcoal-yeast extract (BCYE) agar: selective growth medium for Legionella
      - Fusobacterium: anaerobic, causes oral cavity infections

Importance of Gram-Negative Rods

  • Significance:
      - Particularly critical in patients with predisposing conditions (e.g., immunocompromised)
      - Major contributors to sepsis and endotoxic shock
      - Contains numerous highly antibiotic-resistant strains
      - Generally classified as opportunistic pathogens

Pseudomonas aeruginosa

  • Characteristics:
      - Gram-negative rod
      - Oxidase-positive
      - Non-fermentative; primarily aerobic but can switch to anaerobic metabolism
      - Presence of LPS (lipopolysaccharides) endotoxin typical of other Gram-negative bacteria
      - Exhibits Antiphagocytic properties via exopolysaccharide slime (alginate)
      - Pigments: Often produces fluorescent pigments pyoverdin and pyocyanin

  • Enzymes/Exotoxins:
      - Extensive lytic enzymes including hemolysins, leukocidins, and proteases
      - Exotoxin A: inhibits protein synthesis by ADP-ribosylating translation factor EF-2 (similar to diphtheria toxin)
      - Exoenzyme S: another ADP-ribosyltransferase that transfers ADP-ribose from NAD

  • Infections:
      - Nosocomial infections spread via contaminated equipment, surfaces, and respiratory apparatus
      - Common in immunocompromised individuals, particularly those with cystic fibrosis and post-surgical or burn patients
      - Pseudomonal bacteremia can result in skin lesions termed ecthyma gangrenosum
      - Diagnosis: Culture; characteristic fruity odor and pigment production
      - Treatment: Antibiotics; however, resistance is common in cystic fibrosis patients

Burkholderia

  • Characteristics:
      - Gram-negative rods
      - Oxidase-positive
      - Non-lactose fermenters
      - Motile and aerobic
      - Found ubiquitously in environments like water and soil

  • Species/Pathologies:
      - Burkholderia cepacia: common cause of pulmonary infections in cystic fibrosis patients
      - Burkholderia pseudomallei: endemic to SE Asia and parts of Central/South America, Middle East, Pacific, Africa; causes melioidosis
        - Symptoms include cough, pleuritic chest pain, and skin infections; presents in acute pneumonia and potential septicemia
        - Could function as a biowarfare agent
      - Burkholderia mallei: causes glanders in horses, severe respiratory symptoms, and infection complications

  • Diagnosis: Culture

  • Treatment: Variability in antibiotic effectiveness; resistance is common

Stenotrophomonas maltophilia

  • Characteristics:
      - Formerly classified with Pseudomonas, now recognized separately
      - Gram-negative rod, atmospheric omnipresence
      - Distinguishing feature: production of two inducible metallo-β-lactamases

  • Infections:
      - Primarily opportunistic—affecting immunocompromised individuals via lung infections and indwelling lines

  • Diagnosis: Culture

  • Treatment: Trimethoprim-sulfamethoxazole; resistance encountered with aminoglycosides, penicillins, and third-generation cephalosporins

Legionella pneumophila

  • Characteristics:
      - Gram-negative bacilli, motile, with both oxidase and catalase positive activity
      - Contains over 25 species and 42 serogroups, with L. pneumophila serotype 1 responsible for most infections
      - Aquatic saprophytes that thrive in amoebae and biofilms

  • Transmission: Infection occurs primarily through aerosolized water, such as from HVAC systems, cooling towers, and showers

  • Pathologies:
      - Legionnaires' disease: severe pneumonia that can lead to multi-organ failure if untreated; characterized by non-productive cough, fever
      - Pontiac fever: an epidemic flu-like condition with symptoms lasting several days

  • LPS: Lacks the endotoxic lipid A moiety typically found in Gram-negative bacteria

  • Diagnosis: Grown on Buffered Charcoal-Yeast Extract (BCYE) agar; direct immunofluorescence and specific antibody detection also employed

  • Treatment: Azithromycin for children and fluoroquinolones (e.g., levofloxacin, moxifloxacin) for adults

  • Prevention: Regular maintenance of air conditioning systems and application of biocidal compounds to manage outbreaks

Fusobacterium

  • Characteristics:
      - Gram-negative fusiform bacilli, strictly anaerobic
      - Typically non-lactose fermenting and colonizes oral cavity as commensals
      - Has potent LPS endotoxin and produces various other toxins

  • Pathologies:
      - F. nucleatum: implicated in dental plaque and periodontal disease
      - F. necrophorum: leads to pharyngitis, tonsillitis, and peritonsillar abscesses; can cause Lemierre syndrome, presenting with septic thrombophlebitis due to pharyngeal infections

  • Diagnosis: Anaerobic cultures, PCR

  • Treatment: Several effective antibiotics, though resistant to erythromycin and some strains produce β-lactamase

Summary of Bacteria of Interest

  • Key Species:
      - Pseudomonas aeruginosa
      - Burkholderia (including cepacia and other species)
      - Stenotrophomonas maltophilia
      - Legionella pneumophila
      - Fusobacterium

Pseudomonas aeruginosa Infectious Profile

  • Importance: Notable for widespread infections across body systems, including:
      - Lungs in immunocompromised patients (particularly cystic fibrosis)
      - Skin infections from burns and folliculitis from contaminated water sources
      - UTIs and line-related infections leading to systemic sepsis

  • Environmental Sources: Present in water, medical equipment, and patient care environments

Virulence Factors of Pseudomonas aeruginosa

  • Primary Characteristics:
      - Gram-negative, aerobic, oxidase positive, non-lactose fermenting
      - Notable virulence components:
        - Capsule, slime biofilm
        - Secretion of numerous lytic enzymes
        - Exotoxin A: inhibits ribosomal function impacting protein synthesis
        - LPS endotoxin contributes to various pathogenic processes

Treatment and Resistance Patterns

  • Treatment Challenges: Increasingly multidrug-resistant (MDR); common antibiotics include aminoglycosides and penems, with resistance often noted in cystic fibrosis patients

  • Laboratory Identification: Bacterial cultures yield distinct characteristics: a grape-like scent and pigment production, particularly the blue-green from pyocyanin

Questions and Case Studies

  • Clinical Cases: Utilized in assessing knowledge and application of information regarding Gram-negative rod infections and appropriate treatment strategies:   1. Sepsis from a non-lactose fermenting organism   2. Urinary infections with notable characteristics   3. Wound infection scenarios with methicillin-resistant organisms

  • Educational Focus: Explore resistance mechanisms, appropriate diagnostics, and treatment considerations across different presentations of Gram-negative infections, especially in critically ill or immunocompromised patients.